1. Field of the Invention
This invention relates to an automatic winding mechanism for automatically winding an end of a continuous recording sheet or film around a take-up shaft, for example, in an image forming device, and more particularly to an automatic winding mechanism for a continuous sheet and the like which confirms the presence or absence of a take-up shaft prior to threading of paper to prevent possible failure of an automatic paper threading operation and also to an automatic winding mechanism wherein a continuous sheet can be centered readily with respect to a take-up shaft upon automatic threading of paper.
2. Description of Related Art
A recording sheet or the like for use with an image forming device as disclosed in U.S. Pat. No. 4,806,982, U.S. Pat. No. 4,827,356 or U.S. Pat. No. 4,847,661 is normally provided in the form of a wound roll in a cartridge. Accordingly, when a cartridge is exchanged for a new cartridge, it is necessary to feed a leader portion of a recording sheet drawn out from the new cartridge to a take-up shaft by means of a sheet feeding roller or the like and then to wind the leader portion of the recording sheet around the take-up shaft. Upon such winding, in order for the recording sheet to be automatically wound around the take-up shaft, it is necessary to guide an end of the sheet forwarded to a position near the take-up shaft by a guide means so that the end of the sheet may be properly wound around the take-up shaft.
Conventionally, such guide means is formed either from part of a housing of the image forming device or from four guide members disposed in such a manner as to surround the take-up shaft on all sides, each guide member being mounted for movement in a radial direction to the take-up shaft.
With the type of guide means which is formed from part of a housing, however, since a portion of the housing proximate the take-up shaft is formed as the guide means, there is a limitation in the length (as well as the thickness) of a recording sheet that can be wound around the take-up shaft, therefore when the recording sheet is comparatively long, the guide means cannot be utilized. Additionally, the sheet may not be guided well by this type of guide means, raising the possibility that the sheet may not be wound around the take-up shaft. On the other hand, the guide means which has four guide members is complicated in structure, and since it requires a considerably large amount of space for disposition thereof around the take-up shaft, it cannot be installed where a sufficiently large amount of space cannot be assured.
In addition to the structure described above, a continuous sheet winding device commonly includes a rockable holding arm which is normally urged toward a removable take-up shaft which is rotated to wind a continuous sheet thereon. A roller is supported for rotation in the holding arm for contacting with and pressing against the take-up shaft. Thus, the take-up shaft is rotated to wind a continuous sheet thereon while applying a pressing force against the continuous sheet having a leader portion or the like wound around the take-up shaft by way of the roller supported for rotation on the holding arm.
The conventional continuous sheet winding device, however, commonly includes no means for determining the presence or absence of a take-up shaft. Consequently, even if an operator forgets, for example, the step of loading of the take-up shaft, an automatic paper threading operation is attempted to be performed, but is unsuccessful and therefore must be performed again.
Furthermore, a continuous sheet winding device of the above-described type commonly includes no means for centering a continuous sheet with respect to a take-up shaft upon automatic paper threading. Consequently, if a leader portion of a continuous sheet is transported in a laterally displaced condition by rotation of a transport roller or the like upon automatic paper threading, winding by a take-up shaft will be started in such a condition. This results in the problem that a side edge of the continuous sheet may collide with one of a pair of take-up flanges mounted at the opposite end portions of the take-up shaft and hinder the continuous sheet from being wound properly.